Components in integrated optics, e.g. directional couplers and modulators, may be included in fibre-optic systems for information transmissions. These components include a wafer of optoelectronic material, which has light waveguides diffused into its upper surface. Using, for example, a directional coupler, a transmitted signal can be connected to either of the outputs of the coupler. In general, the components have the disadvantage that light with well-defined polarization is required for this switching to function satisfactorily. If the polarization state is indeterminate, the transmitted signal could be divided between the outputs so that an error in signal transmission occurs in the coupler. A well-defined polarization state in transmitted light signals may be retained if the transmission takes place using optical fibres conserving the polarization state. However, these fibres attenuate the light signals rather heavily and are expensive. The polarization state may also be maintained by the transmitted signals being fed back to their source, which requires a regulating system. These difficulties in transmission may be avoided by making the optical components independent of polarization. In Appl. Phys. letters 35 (10), 15 November 1979 pp 748-750, R. C. Alferness, " Polarization-independent optical direction coupler switch using weighted coupling", there is proposed a polarization-independent optical directional coupler, which, however, requires great accuracy in manufacturing the waveguides. In the Journal of Lightwave Technology, Vol. LT-2 No 1 Feb. 1984, Leon Mc Caughan "Low-Loss Polarisation Independent Electrooptical Switches at .lambda.=1.3 .mu.m" there is proposed a polarization-independent optical coupler which is somewhat simpler than in the reference just mentioned, but which has poorer switching properties. A large, common disadvantage with the optoelectric components according to the two references is that the upper boundary frequency for transmitted light pulses is low. This is due to the light waveguides being oriented in relation to the crystal structure so that the two polarization directions mutually at right angles in a light wave are affected by different refractive indices in the waveguides. The two polarization directions are therefore propagated through the waveguides with different speeds, so that pulse lengthening occurs, which limits the upper pulse frequency.